This invention relates to a system to represent a depth of field in a camera.
In a single-lens reflex camera, the most important feature resides in the fact that a finished condition of a photograph can visually be estimated before actually taken. The feature is based on information relying primarily upon characteristics of a lens system such as a depth of field, framing and so on.
The depth of field is a distance in front of and in rear of a specific object viewed in focus, on a photograph taken with the object focalized. The depth of field is determined depending upon a diameter of a permissible circle of confusion, an aperture value, a lens focal length and a distance to an object (hereinafter referred to as "object distance"). In the single-lens reflex camera, the depth of field can be visually ascertained through a finder, when actually stopping down the lens system to the corresponding aperture value. Since, however, a finder image becomes dark in proportion to the stopping-down, skill is required to estimate the actual finished condition of a photograph on the basis of the finder image. Further, when the lens system is stopped down, roughness of a focusing glass is emphasized, and a pattern of a reflex mirror is seen in a recent multi-function camera. Thus, it is difficult to ascertain the depth of field.
In view of the above circumstances, a display device has conventionally been proposed, as disclosed in Japanese Patent Provisional Publication Nos. SHO62-59935 and SHO62-62335, in which a depth of field capable of being obtained by calculation is displayed as a numerical value or a range. There have been some display devices put into practice. However, further skill is required to estimate an actual finished condition of a photograph, on the basis of the depth of field displayed by the numerals. For example, even if the depth of field is the same, the impression on an actual photograph taken with respect to a near object and that taken with respect to a remote object are entirely different from each other, so that it is difficult to estimate the finished condition of the photograph only on the basis of the depth of field displayed as a numerical value or a range. That is, since the depth of field displayed as the numerical value is a numerical value which is influenced by the above factors, there would arise a great disparity between the numerical value and the impression of the actually taken photograph. After all, the conventional numerical display of the depth of field makes no sense unless the display is corrected on the basis of the user's experience.